1. The Field of the Invention
The present invention relates generally to implantable plates for use bone repair. More particularly, the present invention relates to polymeric plates having polymer molecule orientation for providing strength and non-thermal bendability, and processes and systems for preparing such polymeric plates.
2. The Related Technology
Bones are a vital skeletal feature and provide the frame and structural support for holding associated muscles and other tissue. Additionally, bones, such as the skull bones and ribs, are responsible for protecting vital organs such as the brain, heart lungs, and the like. While bones are structurally strong, they tend to break for various reasons when subjected to excessive forces. Usually, the healing process includes a medical professional aligning the bones on each side of the break so that the regenerated bone material provides a structurally sound mended bone.
In addition to aligning the bone, various stabilizing techniques have been used to retain the broken bone in proper alignment during the healing process. Traditionally, casts have been used to stabilize minor breaks that do not need structural reinforcement at the bone. On the other hand, some complicated fractures or breaks can be susceptible to falling out of alignment during the healing process. As such, plates, pins, bone nails, wires, fasteners, and the like can be used to stabilize the broken bones or fix bone structures. Use of these kinds of structural reinforcement systems during healing have been known to provide bone regeneration and mending.
Due to excellent strength and stability profiles, metallic fasteners and plates have dominated the market for reinforcing breaks or fractures during healing. The most accepted metallic fasteners and plates are biocompatible titanium and/or titanium alloys; however, other types of metallic materials have also been used. Nevertheless, metallic fasteners and plates can be problematic and have some disadvantages.
One disadvantage of implanted metallic fasteners and plates arises from being treated as a foreign body, which sometimes requires the fasteners and plates to be removed. This can occur even if the metallic fastener and plate system is initially well tolerated. As such, the subsequent surgery to remove the metallic fastener and plate system can cause additional trauma to the patient, and adds additional costs to the health care system; especially when the patient has to be hospitalized after the procedure. Additionally, if the metallic fastener and plate system includes an iron component, the irons released from the metallic implant may be found in other organs, which can cause long-term problems.
Another major disadvantage of metallic fastener and plate systems arises from being much stronger than the bone being supported. As such, a broken bone that is fixed with a metallic fastener and plate system may not experience proper loading during the healing process. This is because the metallic repair system can carry a large portion of the load that is normally carried by the bone. As a result, the bone can become weaker over time when the metallic repair system is left in place. Accordingly, after removal of the metallic repair system, the repaired bone may be susceptible to fracturing around the region that was previously supported. Even though the metallic repair system provides structural reinforcement to the healing bone, the bone may develop decreased stability.
To overcome problems with metallic fasteners, fastener and plate repair systems have been fabricated out of various polymeric materials that can be configured into stiff and strong plates. In part, the vast array of different types of polymers have allowed for configuring the plate to be biocompatible. However, a major disadvantage of known polymeric repair systems arises during the implantation process. In contrast to metallic plates, polymeric plates typically cannot be plastically deformed in order to conform to the bone being repaired. In order to achieve adequate bending, heat is often required to soften the polymeric structure and adapt the plate to precisely fit with the geometry of the bone. Numerous processes for heating the plates to allow for such bending have been developed, which include hot air pistols, water baths, heat evolving pillows, laser energy, as well as many forms of heated tips or biopsy instruments. While it is possible to heat and bend a polymeric plate, a significant disadvantage arises due to the additional time and instruments required to implement the surgical procedure. Furthermore, systems such as water baths might face sterility problems.
Additionally, the processes typically used to form fastener holes in polymeric plates have caused anomalous features to develop, which are often sites for potential catastrophic failure. This is because during the injection molding processes pins extend through the mold cavity of the mold to form the fastener holes. As such, the polymeric melt being injected into the mold cavity has to flow around the pins, which have significant diameters in order to accommodate various fasteners. This can result in the melt separating into two melt flows that go around each pin, and each resulting flow has a cooled front portion. When the melt flows that have separated around the pins come into contact again, the significantly cooled front portions of each flow merely weld together instead of providing a homogenous union. The lines that form where the different flows or cooled front portions contact each other again are called joint lines or dwelt lines. Joint lines are a place of potential catastrophic failure, especially when bending the plate.
Therefore, it would be advantageous to have a polymeric plate that is bendable or deformable without heat in order to be contoured to the bone being repaired. Also, it would be beneficial to have a polymeric plate that is configured to provide good initial strength and stability, but also loses some mechanical strength over time so that the bone can self-repair to obtain proper strength and stability characteristics.